Pyongyang criticizes the annual exercises as 'adventurous saber-rattling.' The drills, known as Key Resolve and Foal Eagle, will last 11 days and involve tens of thousands of troops.

Reporting from Seoul — U.S. and South Korean armed forces on Monday began their annual military joint exercises, prompting North Korea to chastise the war games as "a foolish act of banging their heads on a rock."

The 11-day exercises involving tens of thousands of troops are a routine training event designed to improve the ability to defend South Korea, according to U.S.-South Korea Combined Forces Command.

That's not the way Pyongyang sees it. North Korea's official Korean Central News Agency on Monday released a statement calling the drill an "undisguised adventurous saber-rattling [that] is creating such [a] tense situation on the Korean peninsula that a war may break out any time."

In a bit of saber-rattling of its own, North Korea said its armed forces were ready to "blow up the citadel of aggressors once the order is issued," KCNA said.

South Korean officials indicated that they were unconcerned about the threats.

"We consider their condemnation typical, and there's no special response to the criticism," Defense Ministry spokesman Won Tae-jae said in a briefing Monday. "North Korea is well aware of characteristics of the drill."

North Korea said it put all its soldiers and reservists on high alert to "mercilessly crush the aggressors." Officials in Seoul said they had detected no North Korean troop movements in response to the drills.

The exercises, named Key Resolve and Foal Eagle, involve 18,000 U.S. troops and an undisclosed number of South Korean forces. They include live firing, aerial attack drills and urban warfare training. Officials say the drills are defensive in nature.

The international community has moved to further isolate the North Korean regime of Kim Jong Il, which in 2008 dropped out of international talks concerning its nuclear program. Last year, North Korea conducted its second nuclear test and launched a set of missiles.

The North has also tried a bit of diplomatic horse-trading. In January, Pyongyang urged Washington to sign a peace treaty officially ending the Korean War in exchange for nuclear talks. The peninsula is technically still at war because the 1950-53 conflict ended with an armistice and not a peace treaty.

However, the U.S. and South Korea have said the North must first return to the six-party nuclear disarmament talks.

Analysts said they didn't expect North Korea to repeat last year's reaction to the war exercises. Then, it cut off a military hotline between the Koreas.

"After the exercises are over, discussions to restart six-party talks will proceed," said Chang Yong-seok, research director at the Institute for Peace Affairs in Seoul. "It is also possible that Kim Jong Il's visit to China will happen after the drills."

Since Stephen Bosworth, the U.S. representative for North Korea policy, visited Pyongyang in December, envoys in the nuclear talks have held a number of bilateral meetings to try to revive the deadlocked negotiations.

North Korea's chief nuclear envoy, Kim Kye Gwan, plans to visit the United States this month, South Korean Foreign Minister Yu Myung-hwan said last week.

On Sunday, Chinese Foreign Minister Yang Jiechi expressed optimism about the resumption of the talks, adding that none of the countries involved had given up on them.